The isoparaffin/olefin alkylation process is widely used to manufacture a high octane quality blend component for aviation and motor gasoline which is also valued for its relatively low vapor pressure, low sensitivity and, because of its freedom from aromatic components, its environmental acceptability. The process typically reacts a C3 to C5 olefin with isobutane in the presence of an acidic catalyst to produce the alkylate product.
Industrial alkylation processes have historically used concentrated hydrofluoric (HF) or sulfuric acid catalysts under relatively low temperature conditions. Acid strength is preferably maintained at 88 to 94 weight percent by the continuous addition of fresh acid and the continuous withdrawal of spent acid.
Hydrofluoric and sulfuric acid alkylation processes share inherent drawbacks including environmental and safety concerns, acid consumption, and sludge disposal, but in spite of efforts to develop an inherently safe alkylation process, both processes have achieved widespread utilization with the HF process being noted for producing a higher quality product with more favorable unit economics. Although hydrogen fluoride, or hydrofluoric acid (HF) is highly toxic and corrosive, extensive experience in its use in the refinery have shown that it can be handled safely, provided the hazards are recognized and precautions taken. The HF alkylation process is described in general terms in Modern Petroleum Technology, Hobson et al (Ed), Applied Science Publishers Ltd. 1973, ISBN 085334 487 6. A survey of HF alkylation may be found in Handbook of Petroleum Refining Processes, Meyers, R. A. (Ed.), McGraw-Hill Professional Publishing, 2nd edition (1 Aug. 1996), ISBN: 0070417962.
In recent years the design of the HF alkylation reactor has stagnated with no significant changes since the early 1970s. One reactor type widely used in the industry utilizes a shell and tube heat exchanger combined with a sparger system. A typical design is shown in U.S. Pat. No. 3,914,111 (Anderson). In this design, the HF alkylation acid is continuously circulated through the exchanger-reactor past baffles designed to allow a homogenous flow, while the hydrocarbon reactants are dispersed into the liquid in the acid flow direction through spray nozzles installed along a number of spargers which intrude into the reactor at intervals along the length of the reactor from an exterior supply manifold. Similar reactors are shown in U.S. Pat. No. 3,560,587 (Borst), U.S. Pat. No. 3,686,354 (Hervert) and U.S. Pat. No. 4,041,101 (Sobel).
The formation of small droplets of the hydrocarbon reactants in the flowing acid stream is key to the effectiveness of the process. Secondary reactions and loss of product quality can result from less than optimum liquid dispersion and large droplets. The conventional reactor system described above is prone to a number of defects arising mainly from the location and orientation of the spargers with respect to the baffles, including the following:                Inefficient liquid dispersion allows for collision of droplets increasing coalescence and reducing droplet interfacial area, affecting product quality and yields;        Liquid bypassing reduces the interfacial area in the reactor;        Reactor capacity is limited by the number of spargers and nozzles which, in turn is limited by the need to have an inlet port penetrating the reactor shell for each sparger conduit;        Good distribution of sparger nozzles is important to avoid localized high temperatures resulting from the exothermic heat of reaction.        
The present invention has been devised with a view to reducing the extent of these problems in the alkylation reactor. A new type of sparger affords improved droplet dispersion without replacing existing reactors; in fact, existing reactors may be easily retrofitted with the new type of sparger at very low cost.